We measured ingestion by Attwater's pocket gopher (Geomys attwateri) in the coastal prairie of Texas by placing feeding chambers in their tunnels. We constructed a nutrient budget from ingestion, species of plants eaten, and nutrient content of these plants, and we compared it to that for the hispid cotton rat (Sigmodon hispidus), also common in this habitat, and the laboratory rat. Concentration of minerals ingested by G. attwateri appeared sufficient for growth and reproduction. Concentration of protein was lower and concentration of fiber was higher in diets of G. attwateri than in diets of S. hispidus or that was required for laboratory rats. High concentration of fiber reduces digestibility and impedes assimilation of protein. We concluded that protein was likely a limiting nutrient and that a low protein:fiber ratio in the diet during summer could be responsible for the observed decline in reproduction in that season.